The invention relates to a transversely electrically excited atmospheric pressure gas laser (TEA-laser) working in a pulsed mode, with a cooled working gas conducted in circulation, and including a cooled cathode, an anode arranged at a distance thereto, and an open-worked auxiliary electrode arranged between the cathode and the anode.
In gas lasers a plasma obtained by means of a glow discharge is used for generating a coherent electromagnetic radiation with wave lengths that correspond to light from ultraviolet to infrared. With modern TEA lasers, preferably CO.sub.2 lasers, the gas is ionized by an electrical current flowing perpendicular to the beam diffusion direction. This current is supplied and conducted away through two parallel, planar electrodes between which the plasma is evenly distributed, thus giving off more energy to the plasma than is required for ionization. The excess energy partly is transformed into coherent electromagnetic radiation when two mirrors are provided to feedback the radiation amplified by the excited gas molecules. The resulting radiation output increases with a larger electrode surface, a greater electrode distance and a higher gas pressure. The latter, however is upwardly limited by the fact that, when a pressure of approximately 100 mbar is exceeded, the glow discharge, which initially homogenously fills up the volume between the electrodes, will develop into an arc discharge with a sufficiently high current flowing in only a narrow channel. Thereby only a much smaller plasma volume will be available for the generation of laser radiation, the effectiveness being no longer satisfactory (cf. e.g. w. W. Duley, CO.sub.2 -Lasers, Effects and Applications, Academic Press, New York, S. Francisco, London 1976, pages 15 to 72).
For preventing the development of an arc discharge, subdivided electrodes are frequently used with relatively high pressures. In such a case, however discharge instabilities occur, which instabilities can be prevented only by high ohmic pre-resistors at each electrode part, thus necessitating very high operational voltages. Another possibility already put into practice consists in that a principal electrode is designed as a grid and an auxiliary electrode covered with an insulating layer is arranged behind the grid beyond the main discharge volume. If a very high voltage is applied between this auxiliary electrode and the grid, a corona discharge will form, evenly coating the grid. If voltage pulses are applied between the grid and the other principal electrode, a glow discharge will form for the duration of the pulses, evenly filling up the main discharge volume. The disadvantage of this arrangement also is the very high voltage demand.
In U.S. Pat. Nos. 3,940,710 and 3,848,202 three-electrode arrangements are disclosed, each having open-worked auxiliary electrodes arranged between the cathode and the anode. The cathodes of the lasers according to the U.S. patents are pin-shaped and are called "pins". Between the individual pins and a hole located thereabove in the auxiliary electrode, inhomogenous discharges form that affect the formation of a large-area homogenous glow discharge.